1. Technical Field
The present invention relates in general to nanoimprinting and, in particular, to an improved system, method, and apparatus for configuring a membrane, pad, and stamper architecture to achieve a uniform base layer and uniform nanoimprinting pressure.
2. Description of the Related Art
Nanoimprinting technology has developed into a high profile technology that provides a pathway to the next generation of lithography. The features of nanoimprinting, such as pillars, pits, and tracks, are on the order of about 10 nm in diameter and/or width. The capability of transferring these nano-scaled features from a template, mold, or stamper to a substrate has been vigorously demonstrated. A master is typically used to generate the templates, and the templates are then used for mass imprinting production to avoid damage to the valuable master in any imprinting accident. Moreover, the potentials for nanoimprinting in high throughput and low manufacturing cost could trigger a paradigm shift in today's optical lithography technology.
It is important for nanoimprinters to be able to achieve a reasonably uniform pressure along the contact interface so that the pattern built on the template can be uniformly imprinted onto substrates. In other words, an intimate contact simply due to high pressure may be enough to generate a uniform pattern transfer and possibly keep good fidelity of the imprinted features. However, a uniform pressure contact is required to generate not only uniform pattern transfer, but also uniform base layer thickness distribution across the imprinting zone. For example, FIG. 1 schematically illustrates a typical imprinting configuration that includes a mold/stamper/template 11 having a feature pattern 13 that forms imprinted features 15 in a resist layer 17 with a base layer 18 on a substrate 19.
The base layer thickness and uniformity is the parameter that nanoimprinting technology tries to control and perfect. Because the imprinted resist layer is acting as a etch mask for the follow-up reactive ion etch (RIE) step in the nanoimprinting process, the quality of the base layer uniformity is directly linked to the quality of the etched result.
FIG. 2 depicts the differences in the uniformity of the base layer thickness even with the same fidelity of the imprinted pattern features. The top imprint 21 is sufficient for some applications (i.e., no further processing is required), such as in the compact disc (CD) or DVD stamping business, where good fidelity of the imprinted features is the only requirement and base layer uniformity is unnecessary. See, for example, Japanese Patent JP2004330680.
However, in nanoimprinting lithography, the uniformity of the base layer becomes critical and the uniformity of bottom imprint 23 is necessary. However, the bottom imprint 23 is only possible with further processing by etching through the imprint to directly transport the pattern to the substrate. Various types of nanoimprinting tooling have been developed and commercialized. Unfortunately, in order to achieve uniform imprinting pressure, either very complicated gimbaling fixtures or much higher imprinting pressure is typically employed.
Yet another problem is encountered at the edges of the disk substrate (i.e., “edge effects”) due to stress variation along the disk radial direction. As shown in FIG. 3, a conventional imprinting contact configuration comprises a substrate vacuum chuck 41 to which is mounted substrate 19. The stamper 11 is supported by a gel pad 43 and Mylar membrane 45 which extends across an opening in a fixture 47. Air pressure is applied to the membrane 45 to press the stamper 11 against substrate 19. As shown in FIG. 4, this design produces an approximately 50% variation in contact pressure in the radial direction across the imprinted zone 55 with the gel pad (plot 51) or without the gel pad (plot 53). Although these solutions are workable, an improved solution would be desirable.